Introduction to Virginia's Karst
Introduction to Virginia’s Karst A presentation of The Virginia Department of Conservation and Recreation’s Karst Program & Project Underground Karst - A landscape developed in limestone, dolomite, marble, or other soluble rocks and characterized by subsurface drainage systems, sinking or losing streams, sinkholes, springs, and caves. Cross-section diagram by David Culver, American University. Karst topography covers much of the Valley and Ridge Province in the western third of the state. Aerial photo of karst landscape in Russell County. Smaller karst areas also occur in the Cumberland Plateau, Piedmont, and Coastal Plain provinces. At least 29 counties support karst terrane in western Virginia. In western Virginia, karst occurs along slopes and in valleys between mountain ridges. There are few surface streams in these limestone valleys as runoff from mountain slopes disappears into the subsurface upon contact with the karst bedrock. Water flows underground, emerging at springs on the valley floor. Thin soils over fractured, cavernous limestone allow precipitation to enter the subsurface directly and rapidly, with a minimal amount of natural filtration. The purer the limestone, the less soil develops on the bedrock, leaving bare pinnacles exposed at the ground surface. Rock pinnacles may also occur where land use practices result in massive soil loss. Precipitation mixing with carbon dioxide becomes acidic as it passes through soil. Through geologic time slightly acidic water dissolves and enlarges the bedrock fractures, forming caves and other voids in the bedrock. Water follows the path of least resistance, so it moves through voids in rock layers, fractures, and boundaries between soluble and insoluble bedrock.
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